Proximity‐Encirclement of Multiple Exceptional Points in Non‐Hermitian Photonic Waveguides.

Conventionally, dynamical encirclement of exceptional points in non‐Hermitian systems is known to manifest a counterintuitive chiral state conversion. However, the prerequisite of such traits enclosing an exceptional point is broken when only encircling its proximity, preserving a still chiral switching. Research on the proximity‐encirclement in multistate systems is lacking. In this paper, a photonic‐waveguide‐array non‐Hermitian system is proposed to investigate the dynamics by encircling two exceptional points or their proximity. A series of encircling trajectories defined by the parametric equations are designed to steer the evolution of photonic modes in waveguides. The wave propagating along the waveguides is also simulated to capture this non‐Hermitian physics. The chiral behavior in proximity‐encirclement contrasts with the familiar encirclement of one exceptional point and exhibits the unexpected occurrence of nonadiabatic transitions. Furthermore, if two exceptional points are sufficiently encircled, the system will evolve to a stable final state earlier, as a symbol of the occurrence of the nonadiabatic transition. Such novel chiral conversion is maintained only if the encircling trajectories are located at adequate proximity. [ABSTRACT FROM AUTHOR]